What steps can be taken to prevent security vulnerabilities when using external variables in PHP scripts?

To prevent security vulnerabilities when using external variables in PHP scripts, it is crucial to sanitize and validate user input to prevent SQL injection, cross-site scripting (XSS), and other attacks. One way to achieve this is by using functions like filter_var() or htmlentities() to sanitize input before using it in your scripts. 

// Example of sanitizing user input using filter_var()
$user_input = filter_var($_POST['user_input'], FILTER_SANITIZE_STRING);

Keywords

SQL injection cross-site scripting input validation prepared statements secure coding practices

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